Assessment of occupational exposures is a crucial factor in evaluating dose-response relationships and most studies conducted by the Section have an extensive exposure assessment component. Major assessment efforts in cohort studies have involved exposures to acrylonitrile, organic solvents, pesticides, formaldehyde, benzene, xylene, toluene and diesel fumes. In the case-control design, jobs have been evaluated for a wide variety of exposures, including chlorinated hydrocarbons and other solvents, dusts, asbestos, formaldehyde, electromagnetic fields, physical activity, nitrosamines, polycyclic aromatic hydrocarbons, pesticides and cadmium. These exposures have been evaluated in studies of cancer of the peritoneum, breast, kidney, colon, stomach, nasopharynx, esophagus, pancreas, prostate, brain, and lymphatic and hematopoietic system and for studies of parental occupation and childhood cancers. Sixty-three job-specific questionnaires have been developed for a new case-control study of bladder cancer that allow collection of detailed information on specific jobs. Methodologic studies are also conducted to improve exposure assessment techniques and to understand exposure patterns. Job exposure matrices (JEM) assigning a level, probability and exposure profiles have been developed for several occupational exposures. Differences of level of formaldehyde exposure between whites and African Americans were examined.